1. Field of the Invention
The present invention relates to a magnetic-drive device for rotary machinery for transferring or agitating fluids with an impeller driven by rotary motion transmitted from a driving motor through a magnetic coupling means, and more particularly relates to a magnetic-drive device for rotary machinery, having a magnetic coupling means comprising a partition having a novel structure.
2. Related Art Statement
Heretofore, various rotary machines have been employed for transferring, agitating or mixing of chemical fluid materials in the chemical industry. Among those machines, a magnetic-drive centrifugal pump coupled magnetically with and torqued by a driving motor through an interposed cylindrical partition, usually has no shaft sealing means, wherefore any leakage of the liquid being delivered would not occur, so that such pumps have been widely used for transporting liquids such as chemical medicines, petroleum, beverages and the like.
In such a machine, the magnetic coupling can be accomplished by an external driving means comprising a driving magnet arranged concentrically around a driven annular magnet provided on an impeller, an internal driving means comprising a driving magnet arranged inside a driven magnet, or a disc coupling means comprising a driving magnet facing a driven magnet, both magnets being arranged in respective planes perpendicular to the axis of rotation.
Further, those parts which come into contact with liquids, i.e. an impeller, rotor and casing, are made of high quality metal, plastics, ceramics or a plastic-coated or -lined metal that is chemical corrosion-resistant.
Such a magnetic-drive device as used for a centrifugal pump is generally required to fit specifications with repsect to, for instance, corrosion-resistance, pressure-resistance, heat-resistance, etc. of rotary machines to be connected with the device, and further desired to be formed in a compact size as well as to have an increased torque to be transmitted.
If, in order to increase the output of rotary machines such as a pump pressure, the partition is designed with a thickness augmented so as to endure such as increased pump pressure, then not only can compaction be attained but the following problems also will be encountered.
Namely, more eddy current is induced in the magnetic coupling means corresponding to the increment of thickness of the partition and consequently a heat generation loss will result. The heat generation loss lowers the torque transmitting efficienty of the magnet, while it will badly affect fluids being treated and moreover bring about thermal deformation or stress as well as deterioration of corrosion-resistance the of the partition itself. A temperature increment of treated fluids corresponding to the heat generation loss may at times exceed 5 degrees C., so that conventional pumps have been unemployable for such fluids as to undergo chemical changes or the like at an elevated temperature.
If, in order to obviate the influence of the heat generation, the partition is provided with a cooling means comprising, for instance, an increased amount of fluid flow between the rotor and the partition, or a coolant flow through the inside of the partition, itself the distance between the driving magnet and the driven impeller magnet must be increased thereby consequently decreasing the transmitted torque.
As is described above, there have not been any conventional magnetic-drive devices for rotary machinery which could be formed in a compact size, concurrently fitting specifications of requirements for rotary machines.